Flexible vacuum bags are often used to compact and consolidate composite part layups during curing. These bags comprise an oxygen impermeable film such as nylon which sometimes develops leaks during the curing cycle. Bag leaks are difficult to detect and, if not quickly repaired, may result in parts that do not exhibit the desired mechanical properties.
A variety of techniques and equipment have been devised in the past to detect leaks in vacuum bags, but each may have disadvantages. For example, known leak detection techniques may require specialized equipment and/or operators, may be time consuming, may be less than completely reliable and/or may be impractical to use on relatively large parts.
One known technique for detecting bag leaks is performed by moving an ultrasonic listening device over the surface of a part. Leaking air may often cause a high pitch noise that can be detected by the listening device in order to identify the location of the leak. Another known leak detection technique uses helium leak detection equipment comprising a helium source and a helium detector. The helium source is moved slowly over the surface of the bag, while the helium detector is used to sense helium traveling from the source through the bag leak, thereby marking the location of the leak.
In the food industry, colorimetrc dyes have been used to detect air leaks in food packages in order to provide an indication that the packaged foods may be subject to spoilage. These colorimetric dyes are in the form of ink that is applied inside the food packaging, and which change color on exposure to oxygen, thereby providing a visual indication that the package contains a leak.
Accordingly, there is a need for a method and device for detecting leaks in vacuum bags used to process composite parts such as composite layups that avoids the need for specialized detection equipment and which provides a rapid visual indication of the location of bag leaks.